1. (Field of the Invention)
The present invention relates to an alignment layer capable of conferring alignment functions on liquid crystals by a non-rubbing treating means using a simple optical alignment device and to a liquid crystal display using such alignment layer.
2. (Description of the Related Art)
A liquid crystal cell has a pair of glass substrates confronting to each other and an alignment layer disposed on an inner surface of each substrate to give alignment to liquid crystal molecules charged between the substrates. As conventional typical processes for manufacturing an alignment layer, the following 2 processes are known. In the first process as shown in FIG. 14, a photosensitive polymer 52 such as polyimide is applied onto a substrate 51, and its surface is rubbed with a rubbing drum 53 having. a nylon or polyester fiber-planted cloth wound on it, whereby very fine grooves are formed on the surface of the polymer 52. The second process is a SiO slanting deposition process in which silicon oxide (SiO) is vapor deposited in a slanting direction onto a substrate.
In the first process, however, fine dusts are generated or an electric discharge occurs due to static electricity upon rubbing the surface of polymer 52 with the rubbing drum 53, thus causing inconvenience in producing liquid crystal panels. In the second process, an angle of deposition to a substrate as well as the uniformity of layer thickness is difficult to maintain, and further a manufacturing device of large scale is required.
Under these circumstances, the present inventors proposed an alignment layer for liquid crystal displays (also referred to hereinafter as LCD) using a polymer whose photo-reaction is selectively induced by irradiation with linear polarized ultraviolet light (also referred to hereinafter as linear polarized light), as well as a process for producing the same (JP-A-10-87859). This polymer makes use of that shown in the following chemical formula C60: 
whereinxe2x80x94R1=xe2x80x94CnH2n+1(n=0 to 5), k=1 to 12, m=1 to 12; R2=none, xe2x80x94COO, xe2x80x94OCOxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94C6H4xe2x80x94; and xe2x80x94R3 to R7=xe2x80x94H, halogen group or alkyloxy group such as methoxy group. Further, the portion surrounded by the broken line is a cinnamate group or its derivative.
In the case of the alignment layer described above, however, it is necessary to convert natural light directly into linear polarized light with which the polymer is to be irradiated. As a dichroic polarizer used in such conversion into polarized light, a sheet prepared generally by primarily drawing PVA (polyvinyl alcohol), then impregnated it with I(iodine) and sandwiching it between TAC (triacetyl cellulose) is known. However, this dichroic polarizer is poor not only in transmittance in the UV range but also in thermostability, so it cannot be used as an optical alignment device. For this reason, a birefringence-type prism is used to polarize light in the UV range. However, since the birefringence-type prism makes use of a natural crystal of calcite as the prism, it is difficult to obtain a large prism through which the whole area of a substrate used in LCD is irradiated with light. Furthermore, when this prism is used, a optical alignment device is rendered complicated and large.
Accordingly, the object of the present invention is to provide an alignment layer capable of conferring alignment functions on liquid crystals by a non-rubbing treating means in a simple optical alignment device without generating fine dusts or causing an electric discharge by static electricity, as well as a liquid crystal display using the same.
To accomplish the object described above, the alignment layer according to the first aspect of the invention is obtained by applying onto a substrate a polymer having side chains with a mesogen structure and irradiating this applied polymer with ultraviolet light. This mesogen structure is a structure having a group capable of forming liquid crystals.
The alignment layer according to the second aspect of the invention is obtained by applying onto a substrate a polymer shown in formula C4 with side chains having at least one of the mesogen structures shown in formulae C1 to C3 and with the main chain being at least one of homopolymers or copolymers of hydrocarbon, acrylate, methacrylate and siloxane, and irradiating this applied polymer with non-polarized ultraviolet light. 
In formula C1 to C4, x:y:z=100 to 0:100 to 0:99 to 0 whereupon x+y+z=100; n=1 to 12, m=1 to 12, j=1 to 12, k=1 to 12; X, Y, Z=none, xe2x80x94COO, xe2x80x94OCOxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94Cxe2x95x90Cxe2x80x94 or xe2x80x94C6H4xe2x80x94; xe2x80x94R1 to R10=xe2x80x94H, halogen group, or alkyloxy group such as methoxy group, and xe2x80x94R11=xe2x80x94H, xe2x80x94CN, or alkyloxy group such as methoxy group.
This branched-chain polymer has at least one substituent group such as biphenyl, terphenyl, phenyl benzoate and azobenzene as a mesogen component in the side chains thereof, and hydrocarbons, acrylates, methacrylates and cyclohexane in the main chain. As necessary, the polymer can have a structure having photosensitive groups such as cinnamate group or its derivatives added to the mesogen component in the side chains, or a structure to which side chains having and not having photosensitive groups are added together at a predetermined proportion.
The alignment layer described above is obtained easily by applying the polymer onto a substrate and irradiating it with natural light (also referred to hereinafter as non-polarized light). That is, by irradiating the polymer with natural light, the side chains in the polymer are crosslinked with one another (dimerization) to form an alignment layer indicating a pre-tilt angle when used for liquid crystals. Further, since the alignment layer in the first and second aspects of the present invention is obtained by the use of natural light, a polarizer such as birefringence-type prism is not necessary. Accordingly, the optical alignment device can be simplified to form the alignment layer easily. Then, this alignment layer can be used effectively in liquid crystal displays.
Furthermore, by controlling the direction and amount of irradiation of light, it is possible to arbitrarily set the direction of alignment of liquid crystal molecules and the degree of the pre-tilt angle in the alignment layer. Accordingly, the product can be used as an alignment layer in various liquid crystal displays in e.g. TN, VA and IPS modes.
Furthermore, by partial irradiation through a mask, an alignment layer with different pre-tilt angles and alignment directions can be formed on the same substrate. In particular, the expression of a state of alignment of liquid crystal molecules with low and high pre-tilt angles in 1 picture element or the picture-dividing alignment of inverting the alignment of liquid crystal molecules in 1 picture element is an effective means for enlarging a viewing angle in liquid crystal displays. According to the first and second aspects of the invention described above, the picture-dividing alignment is feasible, thus enlarging the viewing angle of a liquid crystal display. Furthermore, the present invention is advantageous for production of liquid crystal displays because fine dusts or an electric discharge due to static electricity upon physical rubbing of the surface of a polymer with a rubbing drum do not occur, and a large manufacturing device is not necessary.
The alignment layer according to the third aspect of the invention is obtained by applying onto a substrate a polymer having at least one of the photosensitive groups shown in formulae C11 to C14 and irradiating the photosensitive groups shown in formulae C11 to C14 and irradiating this applied polymer with non-polarized, linear polarized or partially polarized ultraviolet light. Here, the term xe2x80x9cpartially polarizedxe2x80x9d refers to a state of low degrees of polarization as a whole in which a completely linear polarized component and a non-polarized component are present together, and this partially polarized light can be obtained by the use of the device shown in FIG. 11 below. 
wherein, in formulae C11 to C14, xe2x80x94R1 to R5=xe2x80x94H, halogen group, or alkyloxy group such as methoxy group; xe2x80x94R6 to R9=-H, xe2x80x94CN, phenyl group, phenoxy group, alkyl group such as methyl group or alkyloxy group such as methoxy group.
In a preferred embodiment of the third aspect of the invention, the orientation film is obtained by applying onto a substrate a homopolymer or having at least one of the structures W1 and W2 shown in formulae C11 to C14 above and with the main chain being at least one of hydrocarbon, acrylate, methacrylate and siloxane, and irradiating this applied polymer with non-polarized, linear polarized or partially polarized ultraviolet light. 
wherein, in formula C15 to C17, x:y=100 to 0:0 to 100 whereupon x+y=100; n=1 to 12, m=1 to 12, j=1 to 12; X and Y=none, xe2x80x94COO, xe2x80x94OCOxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94Cxe2x95x90Cxe2x80x94 or xe2x80x94C6H4xe2x80x94; and W1 and W2 are the same as shown in formulae C11 to C14.
According to the third aspect of the invention described above, the polymer contains cinnamylidene (or its derivative), and this polymer is applied onto a substrate and irradiated with non-polarized, linear polarized or partially polarized ultraviolet light whereby the crosslinking reaction (dimerization reaction) accompanied by formation of a cyclobutane linkage as shown in reaction formula C18 below is generated when the polymer of formula C13 above (xe2x80x94R1 to R9=xe2x80x94H) is used, and a good alignment layer indicating a pre-tilt angle upon conversion into liquid crystals is thus obtained. Because this alignment layer can be obtained by irradiation with natural light, no special polarizer is necessary and the optical alignment device can be simplified to form the alignment layer easily. Further, even if linear polarized ultraviolet light is used, the alignment layer can be easily obtained in a short time by using low irradiation energy i.e. a small source of irradiation, and accordingly, the optical alignment device can be simplified. Then, this alignment layer can be used effectively in a liquid crystal display. Further, since this alignment layer can be obtained by a non-rubbing means, neither fine dusts upon formation of the layer nor an electric discharge due to static electricity occurs. This is advantageous for production of liquid crystal panels. 
The rectangular portion shown in reaction formula C18 indicates a molecular chain containing a mesogen component through which the main chain of the polymer binds to its side chain.
The alignment layer according to the fourth aspect of the invention is obtained by applying onto a substrate a polymer having at least one of the structures shown in formulae C31 to C34 and irradiating this applied polymer with non-polarized, linear polarized or partially polarized ultraviolet light. 
wherein, in formulae C31 to C34, xe2x80x94R1 to R3=xe2x80x94H, halogen group, or alkyloxy group such as methoxy group; and xe2x80x94R4 and R5=xe2x80x94H, xe2x80x94CN, or alkyloxy group such as methoxy group.
In a preferred embodiment of the fourth aspect of the invention, the alignment layer is obtained by applying onto a substrate a homopolymer or copolymer shown in formula C37 with side chains of a structure shown in formula C35 or C36 having at least one of the structures W3 and W4 shown in formulae C31 to C34 above and with the main chain being at least one of hydrocarbon, acrylate, methacrylate and siloxane, and irradiating this applied polymer with non-polarized, linear polarized or partially polarized ultraviolet light. 
wherein, in formula C35 to C37, x:y=100 to 0:0 to 100 whereupon x+y=100; n=1 to 12, m=1 to 12, j=1 to 12; X and Y=none, xe2x80x94COO, xe2x80x94OCOxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94Cxe2x95x90Cxe2x80x94 or xe2x80x94C6H4xe2x80x94; and W3 and W4 are the same as shown in formulae C31 to C34.
In the fourth aspect of the invention described above, the polymer contains a mesogen component and a photosensitive group such as xcex2-(2-furyl)acryloyl (or its derivative) group. When this polymer is applied to a substrate and irradiated with non-polarized (natural light), linear polarized or partially polarized ultraviolet light, the xcex2-(2-furyl)acryloyl group undergoes crosslinking reaction accompanied by formation of a cyclobutane linkage as shown in reaction formula C38 below, and a good alignment layer indicating a pre-tilt angle upon conversion into liquid crystals is thus obtained. Because this alignment layer can be obtained by irradiation with natural light, the optical alignment device can be simplified to form the alignment layer easily. Further, even if linear polarized ultraviolet light is used, the alignment layer can be easily obtained in a short time by using low irradiation energy i.e. a small source of irradiation, and accordingly, the optical alignment device can be simplified. Further, since this alignment layer can be obtained by a non-rubbing means, neither fine dusts upon formation of the layer nor an electric discharge due to static electricity occurs. Furthermore, this alignment layer can also be used effectively in a liquid crystal display. 
The rectangular portion shown in the reaction formula C38 is a molecular chain containing a mesogen component through which the main chain of the polymer is bound to its side chain.
The alignment layer according to the fifth aspect of the invention is obtained by applying a homopolymer or copolymer having at least one of the structures shown in formulae C41 and C42 onto a substrate, and irradiating this applied polymer with linear polarized or partially polarized ultraviolet light. 
wherein, in formulae C41 and C42, Ar is p- or m-phenylene groups and/or p- or m-biphenylene groups substituted at the para- or meta-position; and R1 and R2 are hydrogen group, methyl group and/or nitrile group.
The alignment layer according to the sixth aspect of the invention is obtained by applying a homopolymer or copolymer having at least one of the structures shown in formulae C43 to C46 onto a substrate, and irradiating this applied polymer with linear polarized or partially polarized ultraviolet light. 
wherein, in formulae C43 to C46, Ar1 to Ar4 are p- or m-phenylene groups and/or p- or m-biphenylene groups substituted at the para- or meta-position; R1 to R8 are hydrogen group, methyl group and/or nitrile group; X and Y are aliphatic polyester, aliphatic polyether and/or aliphatic polycarbonate; and n=1 to 12, m=1 to 12.
In a preferred embodiment of the sixth aspect of the invention, the alignment layer is obtained by applying a copolymer containing both a component having at least one of the structures shown in formulae C43 to C46 and a component consisting of polyalkylene oxide onto a substrate, and irradiating this applied polymer with linear polarized ultraviolet light.
The polymers used in the fifth and sixth aspects of the invention can be synthesized by coupling of an aromatic acid component having a photo-crosslinking unsaturated bond, a polyether having reactive groups at both the terminals thereof, aliphatic polyester, aliphatic polycarbonate, or a long-chain alkylene component. The basic method for this synthesis can make use of melt polycondensation, solution polycondensation or interfacial polycondensation.
It is necessary that the polymers described above should contain double bonds for photo-crosslinking to express the alignment of liquid crystals. Accordingly, p- or m-phenylene bis(acrylic acid), p- or m-phenylene bis(cyanobutadiene carboxylic acid), p- or m-phenylene bis(cyanoacrylic acid), 4- or 3-hydroxy cinnamic acid, p- or m-biphenylene bis(acrylic acid), p- or m-biphenylene bis(cyanobutadiene carboxylic ccid), p- or m-biphenylene bis(cyanoacrylic acid) etc. are used.
As the component for improving layer formability (polyalkylene oxides) include hydroxyl-terminated polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and propylene oxide to ethylene oxide copolymer-based glycols, amino-terminated polyalkylene oxides such as polyethylene oxide, polypropylene oxide, polytetramethylene oxide, and propylene oxide to ethylene oxide copolymers, and the polyester-type component includes aliphatic polyesters such as polyalkyl adipate, polyalkylene octanoate and polyalkylene sebacate, as well as aliphatic polycarbonates.
The polymer described above is applied onto a substrate and then irradiated with linear polarized or partially polarized light whereby the aromatic acid component having a photo-crosslinking unsaturated bond undergoes the photo-crosslinking reaction shown in the following reaction formula C47, thus readily giving an alignment layer excellent in thermostability. This alignment layer can be obtained by the same non-rubbing treating means as for each preceding aspect of the invention. In addition, even though linear polarized light is used, the alignment layer can be obtained in a short time by using low irradiation energy i.e. a small source of irradiation, and accordingly, the optical alignment device can be simplified to form the alignment layer easily. Furthermore, this alignment layer can also be used effectively in liquid crystal displays. 
The alignment layer according to the seventh aspect of the invention is obtained by irradiating a light-alignment polymer applied onto a substrate with partially polarized ultraviolet light having a completely polarized component mixed with a non-polarized component.
The alignment layer according to the eighth aspect of the invention is obtained by applying a polymer having at least one of the structures shown in formulae C51 to C53 onto a substrate and irradiating this polymer with partially polarized ultraviolet light having a completely polarized component mixed with a non-polarized component. 
wherein, in formulae C51 to C53, xe2x80x94R1 to R9=-H, halogen group, xe2x80x94CN, or alkyloxy group such as methoxy group.
In a preferred embodiment of the eighth aspect of the invention, the alignment layer is obtained by applying onto a substrate a homopolymer or copolymer shown in formula C54 with side chains having at least one of the structures W5 and W6 shown in formulae C51 to C53 above and with the main chain being at least one of hydrocarbon, acrylate, methacrylate and siloxane, and irradiating this applied polymer with partially polarized ultraviolet light having a completely polarized component mixed with a non-polarized component. 
wherein, in formula C54, x:y=100 to 0:0 to 100 whereupon x+y=100; n=1 to 12, m=1 to 12, j=1 to 12; X and Y=none, xe2x80x94COO, xe2x80x94OCOxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94Cxe2x95x90Cxe2x80x94 or xe2x80x94C6H4xe2x80x94; and W5 and W6 are the same as in formulae C51 to C53.
According to the seventh and eighth aspects of the invention described above, the polymer is irradiated with ultraviolet light having a completely polarized component mixed with a non-polarized component, thereby causing the photo-crosslinking reaction of the polymer to readily give an alignment layer exhibiting a pre-tilt angle upon conversion into liquid crystals. That is, when non-polarized ultraviolet light is partially transmitted and partially reflected by an interface between two mediums e.g. air and a transparent plate such as quartz plate, the transmitted light turns into a partially polarized light having a completely polarized component mixed with a non-polarized component. Then, the polymer is irradiated with this partially polarized light whereby an alignment layer can be formed without using any special polarizer. For example, in case the polymer of formula C54 (W5=a structure shown in formula C51, x:y=100:0, n=6, m=2, X=none, and xe2x80x94R1 to R7=xe2x80x94H) is applied onto a substrate and this polymer is subsequently irradiated with non-polarized ultraviolet light from a high-pressure mercury lamp via a slantly arranged transparent plate such as quartz plate, when the angle of incidence of ultraviolet light to the transparent plate is 50xc2x0 or greater, the photosensitive group in formula C54 undergoes dimerization reaction to give an alignment layer exhibiting a pre-tilt angle upon conversion into liquid crystals. This dimerization reaction is a photo-crosslinking reaction accompanied by formation of a cyclobutane bond as shown in reaction formula C55 below. In this reaction, it is necessary to irradiate the polymer with a light having a wavelength at which its photosensitive groups can react. This wavelength varies depending on the type of the polymer but is generally 200 to 500 nm among which a wavelength of 250 to 450 nm is particularly effective. 
The alignment layer described above can be formed by a simple optical alignment device where a transparent plate such as quartz plate is arranged slantly in a light path of a source of irradiation. Further, because the transparent plate having an arbitrary size can be readily obtained, an alignment layer of large area can easily be formed. This alignment layer can also be effectively utilized in liquid crystal displays.